The present invention relates generally to underground bore location systems. Those of ordinary skill in the art should recognize that the term “horizontal bore” refers to the excavation of a hole, typically for utilities or sewers, through the ground and to the excavated hole itself. The present invention relates generally to systems for excavating and locating such bores. Accordingly, unless otherwise indicated, the term “bore” as used herein refers to new bores and to existing buried utilities, sewer lines or similar lines.
Bore location systems are utilized in a variety of circumstances. For example, when horizontal boring systems are used for installing utilities and sewer lines, it is desirable to maintain a directional boring head in a desired boring path and to avoid known obstacles such as existing utilities. Accordingly, systems are known to trace existing utilities from an above-ground position.
A boring head, which may include a boring probe behind a drill head, is underground during use and is therefore not visible to the operator. Accordingly, the boring probe may be configured to transmit signals from the bore that provide location information to an above-ground operator. One system that is configured to determine whether an underground boring probe is laterally offset from its intended horizontal path is described in U.S. Pat. No. 4,881,083, the entire disclosure of which is incorporated herein by reference. This information is used, in turn, to maintain the boring head in its desired path. When drilling underground horizontal bores for installation of water lines that operate by gravity flow, for example sewer lines, greater accuracy in the bore's location and direction is typically needed.